A couple typos found by codespell

.github/PULL_REQUEST_TEMPLATE.md

@@ -7,15 +7,15 @@
 **Description**
 <!-- What is the motivation for this pull request? -->
 <!-- Briefly: what changes are done here? -->
-<!-- If this is to address a Github issue, metion it's number to create a link -->
+<!-- If this is to address a Github issue, mention its number to create a link -->
 <!-- Example: This PR is to fix issue #42 -->
 
 This pull request ...
 
 **Dear reviewer**
 <!-- Let the reviewer and Gammapy team know what you want: -->
 <!-- * Is this ready for review? Or is it work in progress and you want some feedback? -->
-<!-- * Do you want ot go through review here? Or if someone just finish this up and merge it in? -->
+<!-- * Do you want to go through review here? Or if someone just finish this up and merge it in? -->
 <!-- Do you have any specific questions, e.g. about API or implementation? -->
 <!-- Do you include a test executing new code you're adding (to make sure it runs)? -->
 <!-- Do you include some documentation? Is it needed? -->

Makefile

@@ -55,7 +55,7 @@ help:
 	@echo ' * Gammapy code: https://github.com/gammapy/gammapy'
 	@echo ' * Gammapy docs: https://docs.gammapy.org/'
 	@echo ''
-	@echo ' Most common commmands to hack on Gammapy:'
+	@echo ' Most common commands to hack on Gammapy:'
 	@echo ''
 	@echo '     make help          Print help message with all commands'
 	@echo '     pip install -e .   Install Gammapy in editable mode'

docs/development/intro.rst

@@ -70,7 +70,7 @@ Make small pull requests
 
 **Contributions to Gammapy happen via pull requests on Github. We like them small.**
 
-So as we'll explain in mor detail below, the contribution cycle to Gammapy is roughly:
+So as we'll explain in more detail below, the contribution cycle to Gammapy is roughly:
 
 1. Get the latest development version (``master`` branch) of Gammapy
 2. Make fixes, changes and additions locally